Last week O'Reilly went after Jennifer Aniston for her pro-single motherhood comments, but now Bill's taking aim at 29-year-old Kim Kardashian's "Mrs. Robinson"-themed photo shoot with 16-year-old Justin Bieber!

Saying that Kim is "42," (whaterver!) O'Reilly questioned the appropriateness of the shoot on his Fox show.

"I think it's gross," O'Reilly Factor guest Margaret Hoover said during the chat. "It's a 16 year-old having an affair with a celebutante!"

"I will tell you this," Bill added. "If a 16-year-old girl was pictured with a 29-year-old man in any of that, he'd be in big trouble."

But doesn't that happen with male and female models all the time in photo shoots? What's wrong with flipping it around for once!?!?

Check out the behind-the-scenes action from their shoot here: